Dr Tom Dawson, November 2020
The Sars-CoV-2 coronavirus pandemic of 2020 has demanded that people across the globe wear masks or face coverings in many social and working situations to combat the spread of the virus through communities. Many innovators have sought to improve mask performance through a variety of different strategies including reuse, enhanced filtration, breathability, comfort and fit.
One of the strategies used by reusable mask manufacturers has been to integrate antiviral treatments or materials within masks. These additives have both theoretical and laboratory validated antiviral effects against capsulated viruses such as Sars-CoV-2. To date, the author has not identified any mask with purported antiviral properties that has been validated across the full range of real-world environments including normal use, contamination and post wash/dry cycles. Given the risk that Sars-CoV-2 presents to individuals and communities it is critical that claims mask manufacturers make about antiviral and other properties are properly backed up with robust evidence.
The commercial literature citing virucidal benefits covers a large range of compounds with known antimicrobial properties including silver, copper, zinc, silicates, lactoferrins and iron. There have also been industry specific product reviews (1). One important feature that comes out from industry reviews is that the terms antimicrobial, antiviral and antibacterial are often used interchangeably when they clearly have different meanings. Claims (either direct or implied) that antiviral agents effectively kill coronavirus from first use through to multiple uses when integrated into masks are lacking a peer reviewed evidence base.
Independent peer reviews do show that there are promising developments in the fields of antiviral coatings. Most notably a variety of hybrid coatings containing novel combined chemical structures including salt complexes, silicates, silver, copper and zinc have promise in killing capsulated viruses (2, 3, 4). However, there is no direct real-world evidence that the currently available antiviral coatings are suitable for integrating within reusable masks. To address the evidence gap we need to explore effectiveness, durability and potential impacts from bio-contamination.
To determine whether coatings and other integrated materials do indeed function as antivirals in practical use, we must be able to measure effect and use methods that are both scientifically valid and repeatable.
1.) Effectiveness
Both the average killing time and overall level of reduction in active virus particles are heavily impacted by the concentration of virucidal agents within a textile/mask environment. This is the case for both substances that are coated onto (e.g. silicate complexes) or woven into (e.g. copper threads) surfaces. Before any claims are made of specificity of action against SARS-COV-2, or similar encapsulated viruses, the antiviral effectiveness needs to be independently tested utilising the masks and coating method as supplied to end users. The Plaque Assay is accepted by virologists and the peer reviewed literature as a suitable method for determining antiviral effect (5). It has also been validated more recently for determining impact of agents on Sars-CoV-2 activity (6).
2.) Durability
There are reasonable concerns that any wash cycle that is designed to clean away protein-based materials such as blood would also remove protein-based antiviral coatings. If an antiviral mask is going to be supplied for reuse it is important that the manufacturer can back up the claims of effectiveness after repeated washing. A satisfactory protocol would be to test antiviral activity utilising the Plaque Assay after the advertised maximum number of wash/dry cycles. Though this would not fully replicate real world use, it would form a pragmatic standard for validation purposes.
3.) Impact of biocontamination
When a mask is used in either clinical or non-clinical settings there is always the potential for biocontamination. The practicality is that if a coating is itself coated with respiratory mucous, blood or another contaminant, it would likely not be able to contact a virus so this would probably render the coating ineffective. It is important to test the practical performance of masks in real-life situations to ascertain the robustness of the antiviral approach. This includes situations with the products of normal respiration through to where there are high level of contaminants in the user’s environment. This could be simulated in a test setting.
Once effectiveness, durability and the impact of real-world use can be established, clear guidance for use, including guidance on when in the cycle retreating masks with an antiviral might be required, can be formulated. Given the potential dangers from misleading information about mask performance it is important that these factors are measured before masks are supplied that make antiviral claims.
To date the author has not found any mask on the market that meets the evidence required to be able to claim that it effectively kills Sars-CoV-2 in real world use. The author hopes that the commentary above will be the basis for discussions around the development of an industry evaluation framework that will help substantiate the claims around antiviral face masks.
References:
[1] Which consumer review, September 2020 https://www.which.co.uk/news/2020/09/do-antimicrobial-face-coverings-offer-more-protection-against-covid-19/
[2] Balagna et al., May 2020 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7274986/
[3] Powder Coatings, July 2020 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7279752/
[4] Hodek et al., April 2016 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818485/
[5] Timiryasova et al., 2013 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3752766/
[6] Medoza et al., June 2020 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7300432/
